1. Field of the Invention
The present invention relates to a track width error inspector apparatus for detecting errors in the width of recording tracks on a magnetic recording tape.
2. Description of the Prior Art
It is now desired to reduce a width of recording tracks on a magnetic recording tape for implementation of higher density recording. For reducing the width of recording tracks, one of the requirements is to carry out recording on and reproducing from a precise location of the target recording track. In common, the recording on the precise location on a recording track is interrupted by (1) deflection of the recording track and (2) error in the width of the recording track. The track deflection (1) from its original linear course is mainly caused by faulty operation of a recording mechanism or a processing error of a magnetic recording tape. Accordingly, a deflected recording track recorded by one mechanism of the system will hardly be reproduced by another mechanism to impair the system compatibility. Commonly, the track width error (2) results from faulty rewriting on a recording track with gap distance error of a head, heightwise displacement of the head, or eccentric rotation of a cylinder. If there is a track width error during recording, a desired level of signal will unsuccessfully be reproduced regardless of appropriate tracking. Accordingly, elimination of the recording track deflection and the track width error is the most important thing to be tackled for implementation of the forgoing recording track system. In order to eliminate errors of the track, it is necessary to examine the deterioration conditions of recording track error.
For this purpose, a conventional track width error inspector apparatus is provided for visualizing recording tracks on a magnetic tape using a magnetic fluid. The magnetic tape carrying the visualized recording tracks is disposed on a movable table and while it is moved width-wisely of the magnetic tape or of the recording track, its recording tracks are each visually examined or are examined a given number of equal intervals. The borderline of the recording tracks of the magnetic tape can be examined by producing their image on an optoelectric transducer and measuring a change in the voltage associated with the borderline between two adjacent recording tracks in the image (Japanese Laid-open Patent Publication No. 4-41403(1992)). This technique has been introduced for minimizing measuring error in the visual inspection of recording tracks which varies depending on the skill of inspectors and therefore, its principle for inspection is not different from that of the conventional inspection apparatus. The width of each of the recording tracks is measured between the two borderlines and compared with a reference track width to calculate an error in the track width.
The method of the conventional apparatus however takes a considerable length of time to detect the borderlines of the recording tracks since the number of recording tracks over the width of a magnetic tape of the VHS format is as high as 170. Also, for detecting changes in the track width lengthwisely of the magnetic tape, the measuring action has to be repeated several times and also takes a considerable length of time. The narrower the recording track width, the more the care should be taken in measuring the width error in sub micrometer order. Therefore, the accuracy of measurement will be critical. In fact, the conventional visual inspection method permits the error of the acknowledgement of the borderlines and inconsistency between inspectors as high as 1 micrometer. Also, the movement of the table which moves the magnetic tape contains error. Accordingly, the movement of the table should also be executed at a specified accuracy of repeatability and a precision of location.